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The concentrations of 10 metals (Cd, Cr, As, Al, Cu, Pb, Zn, Mn, Hg, and Fe) in 27 groundwater samples collected during different periods (wet, normal, and dry) in the Huixian Karst wetland, the largest subtropical low-altitude karst wetland in China, were detected and analyzed to investigate pollution and health risks. The pollution characteristics, distribution, and health risks of the metals in groundwater were revealed by a comprehensive pollution assessment, multivariate statistical analysis, and health risk assessment model, respectively. The results showed that the average concentrations of metals in groundwater were followed the order of MnFeZnAlHgCrCuCdAsPb. The maximum concentration of Mn (1022.00 μg·L

Carbon sequestration resulting from carbonate rock weathering is closely linked to the global carbon cycle and has turned out to be important in the adjustment of atmospheric CO2 levels. Traditional karst dynamic models based on water–rock–gas interactions underestimate carbon sink fluxes related to carbonate rock weathering because they ignore the utilization of dissolved inorganic carbon (DIC) by aquatic organisms. In this study, a new model based on water–rock–gas–organism interactions was applied in the Pearl River basin, China, to recalculate atmospheric CO2 consumption and to develop an accurate estimation model for carbon sink fluxes at catchment scale. Stable carbon isotope (δ13C) and C/N ratios were used in the counting processes. Data were collected from published literature as well as through field investigation and laboratory analysis. Results show that the Pearl River carbon sink in the Pearl River is 4.31 × 109 kg/a, i.e., 15.8 × 109 kg of atmospheric CO2 per year. Of this, the carbon sink resulting from carbonate rock weathering amounts to 2.14 × 109 kg/a, i.e., 49.7 % of the total. The three largest tributaries of Pearl River, Dongjiang, Beijiang, and Xijiang, respectively absorb 0.5 × 109, 1.19 × 109, and 2.62 × 109 kg of carbon from the atmosphere annually, accounting for 12, 28 and 60 % of the river’s total carbon sink. When compared with the results of previous researches that disregarded the role of aquatic organisms, the new calculation method provides a carbon sink flux value that is 1.2–3.3 times higher, and 1.6 times higher on an average. To improve the calculation accuracy of atmospheric CO2 consumption in global karstic rivers, further research is needed regarding carbon sequestration mechanisms that involve aquatic organisms.

The Wujing River, the largest river in Guizhou Province, is one of the most important water resources for social and economical development. Recently, with the fast population proliferation and rapid economic growth, the drainage basin is intensively interfered by anthropogenic activities. The hydrochemistry of surface water was analyzed from the upper-middle reaches of Wujiang River for investigating the hydrochemical characteristics and their main influencing factors. The results showed that the major cations of the four rivers were Ca²⁺ and Mg²⁺, accounting for more than 70%, and the main anions were HCO₃⁻ and SO₄²⁻, occupying more than 85%. The hydrochemical characteristics in the four rivers were found to be of HCO₃-Ca type, and mainly determined by the carbonate rock dissolution, while only a small proportion of them were of HCO₃ · SO₄-Ca type, reflecting the influence of SO₄²⁻ from anthropogenic activities. Compared to hydrochemical data in 1999, there was an obvious increase in cations and anions concentrations, majorly in NO₃⁻, SO2- ion concentrations, which were significantly affected by human activities. The Na⁺, K⁺ , Cl⁻ in the river mainly came from atmospheric precipitation, and Ca²⁺, HCO₃⁻, Mg²⁺, mainly came from carbonate rocks dissolution, while NO₃⁻ and SO₄²⁻ mainly came from human activities. According to principal component analysis and correlation analysis, hydrochemical composition of Liuchong River was affected by human activity, and that in the upstream of Sancha River was controlled by atmospheric precipitation and the dissolution of carbonate rocks, that to the downstream was enhanced by human activities. The main ion of Maotiao River was controlled by atmospheric precipitation and carbonate rocks dissolution, and also affected by human activity. The Nanming River, the Qingshui river's tributary, was mainly affected by human activity, while the middle and lower reaches of Qingshui River were affected by both the atmospheric precipitation and human activity.